September is a fun time in Major League Baseball. Teams get to expand their rosters from 25 players to 40, making them able to address needs using players from their farm systems. In anticipation of the upcoming flurry of promotions, here is a look at the top 25 players currently in the majors who are younger than 25. To qualify for this list, a player must be 24 years or younger as of Aug. 30 and have at least 50 plate appearances or 50 innings pitched in the majors.

Disagree with the rankings or think I left someone out? Let me know on Twitter or in the comments below.

1. Mike Trout, Los Angeles Angels, OF

The best player in baseball. Including this season, Trout has 26.3 wins above replacement in his first four seasons, sixth most in MLB history.

2. Bryce Harper, Washington Nationals, OF

Through his age-20 season (2012 and 2013), here are the top three players whose batting careers are most similar to Harper’s: Tony Conigliaro, Ken Griffey and Mickey Mantle. Not bad company to be in, not matter how much he has struggled this season.

3. Yasiel Puig, Los Angeles Dodgers, OF

Has hit better than .300 in each of his two seasons, including .301 this year with a .388 on-base percentage and .495 slugging. Puig’s 4.4 WAR is 19th best in majors and he should continue to hit for average and power.

4. Salvador Perez, Kansas City Royals, C

One of the best throwing catchers in the majors, Perez leads his position in defensive runs saved and can swing the bat (0.272 batting average, 0.308 wOBA). He makes contact with regularity but needs to see his walk rate improve from its current 5.5 percent rate.

5. Giancarlo Stanton, Miami Marlins, OF

Stanton has a career batting average on balls in play of .334. His power (.540 slugging and .269 isolated power) makes up for an average arm in right field (1.2 Ultimate Zone Rating).

6. Sonny Gray, Oakland Athletics, P

He has three plus pitches (cutter, curve and changeup) and has a 3.3 strikeout-to-walk ratio in high leverage situations.

7. Jose Fernandez, Miami Marlins, P

Before his injury, Fernandez was one of the best pitchers in baseball. He punched out 70 batters in 51.2 innings and had a 5.4 strikeout-to-walk ratio.

8. Manny Machado, Baltimore Orioles, IF

Before a serious knee injury ended his 2013 season, Machado was one of the best third baseman in baseball with a 5.8 UZR and was just the second player under the age of 21 to hit 50 doubles in a season.

9. Julio Teheran, Atlanta Braves, P

Owner of one of the best changeups in baseball (1.59 runs saved per 100 pitches), Teheran strikes out 7.8 batters per nine innings and has a 3.6 strikeout-to-walk ratio.

10. Christian Yelich, Miami Marlins, OF

This left-handed hitter has a .352 weighted on-base percentage and 128 wRC+ against right-handed pitching and has seen his performance improve against lefties this season (128 wRC+ vs 33 wRC+ in 2013).

11. Freddie Freeman, Atlanta Braves, IF

Freeman has had his ups and downs this season, but he has accumulated 10.7 WAR and 131 wRC+ in his career and only Stanton has been on base more times than Freeman.

12. Wil Myers, Tampa Bay Rays, OF

Last year’s AL rookie of the year took a step back this season largely because of a decrease in BABIP (0.362 last season and  0.277 currently). His true talent is somewhere in between, but there is no reason he can’t put up between three and five WAR per season.

13. Michael Wacha, St. Louis Cardinals, P

Wacha mixes a devastating changeup with an above-average fastball to great effect, striking out 8.6 strikeouts per nine innings and a 3.3 strikeout to walk ratio.

14. Jose Altuve, Houston Astros, IF

Altuve leads the majors in hits (181) and average (.332) and had 41 steals in the first half of the season.

15. Anthony Rendon, Washington Nationals, IF

Rendon has quietly become the best team’s best all-around player. Rendon is 12th in WAR (4.7), the fourth most valuable base runner in the league (7.3 Base Running runs) and has been a solid fielder (six defensive runs saved and a 0.8 Ultimate Zone Rating)

16. Starlin Castro, Chicago Cubs, IF

Castro is hitting .286 in the majors, accumulating 10.9 WAR and posting a 0.320 wOBA. Plus, has drastically reduced his air balls to the opposite field, and he’s turned many of those into pulled flies and liners.

17. Trevor Rosenthal, St. Louis Cardinals, P

His recent struggles and slight loss of velocity aside, Rosenthal is one of the best relievers in baseball. He strikes out more than three batters for every one he walks and has a 2.42 career FIP.

18. Nolan Arenado, Colorado Rockies, IF

Arenado moved quickly through the Rockies’ minor league system and is showing more patience at the plate on balls outside of the strike zone; plus, he doesn’t strike out as much as he did in his rookie season.  A lower groundball-to-fly ball ratio also indicates there may be more power on the horizon.

19. Martin Perez, Texas Rangers, P

His changeup is stellar and his two-seam fastball, which he has thrown more this year, is one of the best in baseball, saving 1.96 runs per 100 pitches thrown.

20. Eric Hosmer, Kansas City Royals, IF

Before he fractured his right hand, Hosmer made contact with 87.7 percent of pitches in the strike zone and had a career 0.141 isolated power.

21. Danny Salazar, Cleveland Indians, P

After being sidelined by Tommy John surgery in 2010, Salazar has bounced back in a big way. The right-hander has pitched 125.2 innings, striking out 145 and walked just 41.

22. Mike Zunino, Seattle Mariners, C

An aggressive hitter, Zunino swings at 73.4 percent of pitches in the strike zone and hasn’t been able to do much with them (84 wRC+) but defensively, he is one of the best catchers in the game.

23. Gerrit Cole, Pittsburgh Pirates, P

Cole has the velocity and the pitch mix to be a number one starter. He just needs them all working at the same time.

24. Jacob Turner, Chicago Cubs, P

Theo Epstein, general manger of the Chicago Cubs, acquired former prospect Jacob Turner on waivers from the Marlins and they have been rewarded with a pitcher who doesn’t walk batters much (6.3 percent of the time) and has a 51.4 percent goundball rate.

25. Jean Segura, Milwaukee Brewers, IF
One of the league’s best base runners, Segura shows the ability to hit for extra base hits despite struggling at the plate this year (0.237 batting average).